Addresses of potential controls where a telephone number was unavailable (because the household was ex-directory) were discarded.
Initially, 625 individuals were identified but 78 (12.5%) were excluded as no telephone number could be traced for them.
They were also given a telephone number so that they could contact the lead researcher if they had any further queries.
They may be a lucky number, a telephone number, a house number, an age, the number of children or grandchildren, or husbands(l).
For each case, two controls were selected from households identified using progressive digit dialling based on the case's home telephone number.
Additionally, a toll free telephone number was provided so that further questions could be answered by a study team physician.
About one year before our research, he visited his place of birth and tracked down his daughter's telephone number.
Respondents with an unlisted telephone number were requested by mail to pass on their number.
